1. Field of the Invention
The present invention relates to an apparatus and process for driving a scanner, and, more particularly, to an apparatus and process able to minimize vibrations and noise generated while reading color images.
2. Description of the Related Art
Generally, a scanner is an electro-optical apparatus that converts the images forming the contents of a document, a picture or a film and the like, into digital data so that the digital data may be either stored in a computer or transferred through a communication circuit. The scanner converts images into graphic files and also converts the contents of a book or a document into character data that can be recognized by the computer driven by proper character recognition software.
The basic operating principle of the scanner depends upon light that is scanned onto the surface of a document such as a cut sheet of a printable medium, so as to generate voltages that vary in proportion to the amount of light reflected from the surface, and then form a pattern of pixels that correspond to the voltage. Scanners are classified as either color scanners or black-and-white scanners, in accordance with the type of image sensor incorporated into the scanner, and are further classified as either a hand-scanner that is held in a user""s hand while being used, a sheet feeding type of scanner in which a document is fed and read like in an ink-jet printer, or a flat bed type scanner, a widely used instrument in which a document is laid upon a glass plate and an image sensor reads the images borne by the surface of the document while the sensor is moved beneath the glass plate.
Flat bed type scanners use a driving motor which moves image sensors across incrementally successive lines of the images. The scanning of colored images requires a step motor that serves as the motive power of the scanner to drive three different light sources for red, green and blue colored components within each line of the images being scanned. Consequently, the scanning time for each line of the image is at least three times slower when scanning colored images than when scanning black-and-white images. Although the step motor used to the image sensors may be driven at high speed when scanning black and white images because the scanning time per line is short, the driving speed of the motor must be reduced by more than one-third when scanning colored images in order to accommodate passage of each of the image sensors. I have noticed that the step motor, as a driving source of the scanner, generates intense vibrations during its low speed mode while scanning colored images. This creates a problem by lowering image quality and, at the same time, causes intense noise to be generated by the vibration while reading colored images.
It is therefore an object of the present invention to provide an improved apparatus and process for converting images into binary data.
It is another object to provide an apparatus and process for driving a scanner to convert both black-and-white and colored images into binary data.
It is still another object to provide a scanning apparatus and process with a stepping motor that is driven at a high speed regardless of whether black-and-white images or color images are being scanned.
It is yet another object to provide an apparatus and process that uses a motor able to drive an image sensor with reduced occurrence of vibration and noise while reading colored images.
These and other objects may be achieved with an apparatus for driving a scanner with a driving motor that is rotated in both directions, a driving gear driven by the driving motor, a driving pulley that rotates a timing belt coupled to the scanner""s body, a reduction gear that engages a gear portion of the driving pulley, a power transmitter that directly transfers rotational force from the driving gear to the driving pulley or transfers the rotational force through the reduction gear to the driving pulley. When reading a colored image, the driving force is decelerated and then transferred to the driving pulley while the driving motor rotates at the same speed as a when reading a black-and-white image, in accordance with the rotating direction of the driving motor.
Preferably, the power transmitting unit includes planetary gears which are engaged with the driving gear so as to revolve on the driving gear in accordance with the rotating direction of the driving gear and selectively engaged with the gear portion of the driving pulley. A connecting arm is rotatably coupled to the driving gear, and the planetary gears are respectively rotatably mounted at both ends of the connecting arm so as to be engaged with the driving gear.
Further, in other aspect of the present invention, there is provided a method for driving a scanner, having the steps of rotating a driving gear by a driving motor; transferring a rotational force of the driving gear to a driving pulley; rotating a timing belt by the driving pulley; driving a scanner body which is coupled to the timing belt, where the driving gear directly transfers a rotational force to the driving pulley when the driving motor is rotated clockwise, and the rotational force of the driving gear is transferred through a reduction gear to the driving pulley when the driving motor is rotated counter-clockwise so that a black-and-white image and a color image are read at an equal speed of the driving motor.